Cavity determination apparatus

ABSTRACT

The invention relates to a cavity determination apparatus for determining a cavity (3) within an object (2), in particular, for determining the location and dimensions of a heart chamber within a person. A bendable segment of an introduction element (5) is arranged within the cavity in different arrangements, wherein curves defined by the bendable segment in the different arrangements are determined by a curve determination unit (7). A cavity reconstruction unit (8) reconstructs the cavity based on the determined curves. Thus, not only single locations within the cavity are acquired and used for reconstructing the cavity, but larger curves. A lot of spatial information can therefore be acquired and used very fast. This allows reconstructing the cavity with improved quality in a relatively short time.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 317 of International Application Serial No. PCT/IB2013/055057, filedon Jun. 20, 2013, which claims the benefit of EP application Serial No.12305719.2, filed on Jun. 22, 2012. This application is herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a cavity determination apparatus, a cavitydetermination method and a cavity determination computer program fordetermining a cavity within an object.

BACKGROUND OF THE INVENTION

US 2010/0268059 A1 discloses an ablation system for ablating cardiactissue. The system comprises an ablation catheter with anelectromagnetic localization sensor located close to the tip of theablation catheter. The tip of the catheter is moved to differentlocations on the inner wall of the heart, wherein at each location theposition of the tip is determined by using the localization sensor. Theresulting set of determined positions is used for reconstructing aninner cavity of the heart.

Since in an acceptable time only few different positions of the tip ofthe ablation catheter within the cavity can be determined, thereconstructed cavity, which is determined based on only these fewlocations of the tip of the ablation catheter, has a poor quality only.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cavitydetermination apparatus, a cavity determination method and a cavitydetermination computer program for determining a cavity within anobject, which allows determining the cavity within the object withimproved quality in a relatively short time.

In a first aspect of the present invention a cavity determinationapparatus for determining a cavity within an object is presented,wherein the apparatus comprises:

-   -   an introduction element for being introduced into the cavity,        wherein the introduction element comprises a bendable segment        for being arranged within the cavity in different arrangements,    -   a curve determination unit for determining curves defined by the        bendable segment within the cavity in the different        arrangements,    -   a cavity reconstruction unit for reconstructing the cavity based        on the determined curves.

Since not only single locations within the cavity are acquired, butcurves defined by the bendable segment within the cavity in thedifferent arrangements, a lot of spatial information can be acquiredvery fast. This allows reconstructing the cavity with improved qualityin a relatively short time.

The determined curve defined by the bendable segment within the cavityin the respective arrangement can be regarded as a one-dimensional linedescribing the shape, orientation and location of the bendable segmentwithin the cavity in the respective arrangement. The determined curvecan therefore be regarded as describing the spatial run of the bendablesegment within the cavity in the different arrangements.

The introduction element is preferentially a catheter, in particular, anablation catheter for ablating an inner wall of the cavity.Preferentially, the cavity is a cavity of a heart of a living being andthe ablation catheter is adapted to ablate cardiac tissue.

In an embodiment the cavity reconstruction unit is adapted toreconstruct the cavity such that the determined curves defined by thebendable segment in the different arrangements are within thereconstructed cavity. Moreover, at least in some of the differentarrangements the bendable segment can be in contact with the inner wallof the cavity such that the curves define contact curves, wherein thecavity reconstruction unit can be adapted to reconstruct the cavitydepending on the contact curves. In particular, the cavityreconstruction unit can be adapted to reconstruct the cavity such thatwalls of the reconstructed cavity correspond to the contact curves. Forinstance, the cavity reconstruction unit can be adapted to reconstructthe cavity such that the walls of the reconstructed cavity run throughthe contact curves and/or enclose the contact curves. This allowsreconstructing the cavity reliably based on the contact curves.

In a preferred embodiment the introduction element comprises at leasttwo electrodes between which the bendable segment is located, whereinthe apparatus comprises a contact determination unit, which iselectrically connected to the at least two electrodes, for determiningcontact information indicating whether the bendable segment is incontact with the inner wall of the cavity based on electrical signalsreceived from the electrodes, wherein the cavity reconstruction unit isadapted to determine whether determined curves are contact curvesdepending on the contact information. The contact determination unit ispreferentially adapted to determine that the bendable segment is incontact with the inner wall of the cavity, if the electrical signalsreceived from the electrodes indicate that the electrodes are in contactwith the inner wall. This allows the apparatus to reliably determinewhether the bendable segment is in contact with the inner wall of thecavity or not in the respective arrangement such that contact curves canreliably be determined.

In some of the different arrangements the bendable segment may not be incontact with the inner wall of the cavity such that the curves definedby the bendable segment are non contact curves, wherein the cavityreconstruction unit can be adapted to reconstruct the cavity dependingon the contact curves and depending on the non contact curves. Thecavity reconstruction unit can be adapted to reconstruct the cavity suchthat the non contact curves are within the reconstructed cavity. Theconsideration also of the non contact curves, while reconstructing thecavity, can further improve the quality of the reconstruction.

The cavity reconstruction unit can also be adapted to determine whetherdetermined curves are non contact curves depending on the contactinformation provided by the contact determination unit. The at least twoelectrodes and the contact determination unit can therefore also be usedto reliably determine non contact curves, which can be used togetherwith contact curves for reconstructing the cavity.

In an embodiment the cavity reconstruction unit is adapted to provide anadaptable cavity model and to adapt the cavity model to the determinedcurves defined by the bendable segment in the different arrangements forreconstructing the cavity. The cavity model may be a generic model or anobject-specific model, in particular, a patient-specific model. It ispreferentially an anatomical model. The cavity model is, for instance, amodel of a cavity of a heart of a living being, which is adapted to, forinstance, the contact curves. The use of the cavity model can furtherimprove the quality of reconstructing the cavity.

The cavity model can be adapted such that the determined curves definedby the bendable segment in the different arrangements are within thecavity model, i.e. such that the determined curves defined by thebendable segment in the different arrangements are enclosed by theadapted cavity model. If at least some of the determined curves definedby the bendable segment within the cavity in the different arrangementsform contact curves, the cavity model can be adapted to these contactcurves such that the contact curves correspond to the outer surface ofthe cavity model. If at least some of the determined curves defined bythe bendable segment within the cavity in the different arrangements arenot contact curves, the cavity model can be adapted to wrap thesedetermined curves. The cavity model can be regarded as a regularization,which can be used to reconstruct the cavity based on a determined set ofcurves defined by the bendable segment within the cavity in thedifferent arrangements. Alternatively or in addition, also anotherregularization can be used. For instance, the cavity reconstruction unitcan be adapted to perform a morphological opening or closing of thedetermined curves defined by the bendable segment within the cavity inthe different arrangements for reconstructing the cavity.

In particular, if the determined curves defined by the bendable segmentare non contact curves, these non contact curves lie within the cavityand the surface of the cavity has to be estimated from these curves. Theregularization preferentially defines which points are likely to bewithin the cavity and which points are likely to be outside the cavitybased on the non contact curves, in order to determine the surface ofthe cavity. This regularization can be model-based, wherein theregularization is performed such that the cavity model, which ispreferentially an anatomical model, wraps the set of non contact curves.If prior anatomical information, i.e. an anatomical cavity model, is notpresent, homogenous mathematical regularization can be used by thecavity reconstruction unit. For instance, a morphological opening of thecurve set can be used for estimating which points lie necessarily withinthe cavity.

In another embodiment the cavity reconstruction unit is adapted tointerpolate the determined curves defined by the bendable segment in thedifferent arrangements for reconstructing the cavity. For instance, itcan be interpolated between contact curves for determining the cavity.The interpolation procedure can use, for example, triangulation,Fourier-based interpolation or another interpolation technique. Thus,the cavity reconstruction unit can be adapted to reconstruct the cavity,without using prior information like an object-specific model.

The interpolation of the determined curves defined by the bendablesegment in the different arrangements for reconstructing the cavity canbe combined with a regularization. For instance, the regularizationcould be performed by switching from an interpolation constrain to anenergy-based fitting of a cavity model. This allows improving thequality of the reconstructed cavity, if the determined curves defined bythe bendable segment in the different arrangements are noisy.

It is preferred that the object is a living being, wherein the cavity isinfluenced by at least one of cardiac motion and respiratory motion,wherein the apparatus comprises a motion signal providing unit forproviding a motion signal being indicative of at least one of a)different cardiac phases and b) different respiratory phases, whereinthe cavity reconstruction unit is adapted to reconstruct the cavitybased on the determined curves defined by the bendable segment and basedon the provided motion signal. By considering the motion signal, i.e.the cardiac signal and/or the respiratory signal, while reconstructingthe cavity, the reconstruction may comprise less motion artifacts.Preferentially, based on the motion signal each determined curve definedby the bendable segment can be assigned to a certain motion phase, i.e.to a certain cardiac phase and/or to a certain respiratory phase,wherein this assigned phase information can be used to reconstruct thecavity with reduced motion artifacts. For instance, the cavityreconstruction unit can be adapted to use curves only, which correspondto the same motion phase, in order to reconstruct a cavity, whichcorresponds to this certain motion phase.

The curve determination unit can be adapted to determine the position ofat least a part of the introduction element being in contact with a partof the living being, which moves in accordance with at least one of thecardiac cycle and the respiratory cycle, over time, thereby determininga movement of the part of the introduction element, wherein the motionsignal providing unit can be adapted to determine the motion signaldepending on the determined movement. For instance, the curvedetermination unit can be adapted to determine the position of anelectrode of the introduction element, while the electrode is in contactwith an inner wall of a heart, over time, thereby determining themovement of the electrode. Since the electrode is in contact with theinner wall of the heart, the movement of the electrode is likely to beperiodic in accordance with the cardiac cycle such that the cardiacsignal can be determined depending on the movement of the electrode.Also the position of another part of the introduction element may bedetermined over time, while this part is in contact with a part of, forinstance, a person moving in accordance with the cardiac cycle or therespiratory cycle, in order to determine the motion signal depending onthe movement of this part of the introduction element. Respiratorymotion may be estimated using the shape of a catheter, while a part ofthe catheter abuts against a part of an anatomy of a person thatexperiences pure respiratory motion or from which respiratory motion canbe estimated. Also a further shape sensing catheter can be used fordetermining respiratory motion in the same way. Moreover, other meanscan be used for providing a motion signal. For instance, anelectrocardiograph can be used for providing a cardiac signal, arespiratory belt can be used for providing a respiratory signal, arespiratory signal can be determined based on an analysis of a videoshowing the moving thorax of a person, et cetera.

The introduction element and the curve determination unit arepreferentially adapted to determine the curves defined by the bendablesegment within the cavity by optical shape sensing. This allows theapparatus to reliably determine the different curves defined by thebendable segment within the cavity, without necessarily requiringfurther localization units like an electromagnetic localization unit oran x-ray localization unit.

In a further aspect of the present invention a cavity determinationmethod for determining a cavity within an object is presented, whereinthe method comprises:

-   -   determining curves defined by a bendable segment of an        introduction element introduced into the cavity in different        arrangements within the cavity by a curve determination unit,        and    -   reconstructing the cavity from the determined curves by a cavity        reconstruction unit.

In another aspect of the present invention a cavity determinationcomputer program for determining a cavity within an object is presented,wherein the computer program comprises program code means for causing acavity determination apparatus as defined in claim 1 to carry out thesteps of the cavity determination method as defined in claim 14, whenthe computer program is run on a computer controlling the cavitydetermination apparatus.

It shall be understood that the cavity determination apparatus of claim1, the cavity determination method of claim 14 and the cavitydetermination computer program claim 15 have similar and/or identicalpreferred embodiments, in particular, as defined in the dependentclaims.

It shall be understood that a preferred embodiment of the invention canalso be any combination of the dependent claims with the respectiveindependent claim.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings:

FIG. 1 shows schematically and exemplarily an embodiment of a cavitydetermination apparatus for determining a cavity within an object,

FIG. 2 shows schematically and exemplarily a tip of a catheter of thecavity determination apparatus, and

FIG. 3 shows a flowchart exemplarily illustrating an embodiment of acavity determination method for determining a cavity within an object.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows schematically and exemplarily an embodiment of a cavitydetermination apparatus for determining a cavity within an object. Theapparatus 1 comprises an introduction element 5 for being introducedinto the cavity 3, wherein the introduction element 5 comprises abendable segment for being arranged within the cavity 3 in differentarrangements. In this embodiment the object is a person 2 lying on atable 4 and the cavity 3 is a chamber of the heart of the person 2.Moreover, in this embodiment the introduction element 5 is an ablationcatheter, wherein the tip 6 of the ablation catheter 5 has beenintroduced into the cavity 3. The bendable segment of the ablationcatheter 5 is located at the tip 6 of the ablation catheter 5 and can bepositioned, i.e. bent, oriented and/or located, within the cavity 3 suchthat it conforms with an inner wall of the cavity 3, in order to bringthe bendable segment into contact with the inner wall.

The cavity determination apparatus 1 further comprises a curvedetermination unit 7 for determining curves defined by the bendablesegment within the cavity 3 in the different arrangements and a cavityreconstruction unit 8 for reconstructing the cavity based on thedetermined curves.

Preferentially, the bendable segment of the ablation catheter 5 isarranged in different arrangements within the cavity 3 such that in atleast some of these arrangements the bendable segment conforms with theinner wall of the cavity 3 and is thus in contact with the inner wall ofthe cavity 3. In this case, the determined curves define contact curves,wherein the cavity reconstruction unit 8 is adapted to reconstruct thecavity depending on these contact curves, i.e. depending on therespective shape, orientation and location of the respective contactcurve. In particular, the cavity reconstruction unit 8 can be adapted toreconstruct the cavity such that walls of the reconstructed cavity aredefined by the contact curves.

The cavity reconstruction unit 8 can be adapted to provide an adaptablecavity model and to adapt the cavity model to the contact curves fordetermining the cavity. Thus, the cavity model, which can also beregarded as being an existing template of the cavity, which may begeneric or person specific, can be fitted to the contact curves. Thecavity model can be arranged and/or deformed such that the walls of thecavity model are defined by the contact curves.

If at least some of the determined curves defined by the bendablesegment within the cavity in the different arrangements are not contactcurves or if, in an embodiment, it is not known whether the determinedcurves are contact curves or non contact curves, the cavity model can beadapted to wrap the determined curves defined by the bendable segmentwithin the cavity in the different arrangements. The cavity model can beregarded as a kind of regularization, which can be used to reconstructthe cavity based on a determined set of curves defined by the bendablesegment within the cavity in the different arrangements. Alternativelyor in addition, also another regularization can be used, in particular,if all determined curves are non contact curves or if it is not knownwhether the determined curves are contact curves or non contact curves.For instance, the cavity reconstruction unit can be adapted to perform amorphological opening or closing of the determined curves defined by thebendable segment within the cavity in the different arrangements forreconstructing the cavity.

The cavity reconstruction unit 8 can also be adapted to reconstruct thecavity by interpolating the determined contact curves, wherein theinterpolation can include, for example, a triangulation, a Fourier-basedinterpolation or another interpolation technique. Thus, the cavity maybe reconstructed “from scratch”, i.e. using the sample shapes, i.e. thesampled contact curves, without any prior data. This kind ofreconstruction relies on the assumption that what constitutes the volumeof the cavity, i.e. the inside of the cavity, can be inferred from thecontact curves.

The interpolation of the determined curves defined by the bendablesegment in the different arrangements for reconstructing the cavity canbe combined with a regularization, in order to improve the quality ofthe reconstructed cavity, particularly if the determined curves definedby the bendable segment in the different arrangements are noisy.

FIG. 2 shows schematically and exemplarily the tip 6 of the introductionelement 5 in more detail. The tip 6 of the introduction element 5comprises several ring electrodes 14 and a cap electrode 13. Theseelectrodes 13, 14 are arranged along the bendable segment 15, whereinthe bendable segment can also be larger than indicated in FIG. 2. Theapparatus 1 further comprises a contact determination unit 9, which iselectrically connected to the electrodes 13, 14, for determining contactinformation indicating whether the bendable segment 15 is in contactwith a wall of the cavity based on electrical signals received from theelectrodes 13, 14, wherein the cavity reconstruction unit 8 is adaptedto determine whether the determined curves are contact curves dependingon the contact information. In particular, the contact determinationunit 9 is adapted to determine that the bendable segment is in contactwith the inner wall of the cavity, i.e. conforms to the inner wall ofthe cavity, if the electrical signals received from all electrodes 13,14 indicate that the electrodes 13, 14 are in contact with the innerwall.

If the electrodes 13, 14 are not in contact with the cardiac tissue ofthe inner wall of the cavity, they substantially do not receive anyelectrical signal, i.e. the output of the electrodes is mostly flat. Ifthe electrodes are in contact with the cardiac tissue, they detect aperiodic electrical signal. Based on these differences in electricaldetection the contact determination unit 9 can determine whether allelectrodes 13, 14 and, thus, the bendable segment 15 are in contact withthe inner wall of the cavity, i.e. whether the bendable segment 15conforms to the inner wall of the cavity.

In some of the different arrangements the bendable segment may notconform to the inner wall of the cavity 3 and may therefore be not incontact with the inner wall such that the determined curves are noncontact curves, wherein the cavity reconstruction unit 8 can be adaptedto reconstruct the cavity also depending on the non contact curves. Inparticular, the cavity reconstruction unit 8 can be adapted toreconstruct the cavity such that positions of the non contact curves arewithin the reconstructed cavity. For determining the non contact curves,the electrodes 13, 14 can be used, which are also used for determiningthe contact curves. In particular, the cavity reconstruction unit can beadapted to determine whether determined curves are non contact curvesdepending on the contact information provided by the electrodes 13, 14,wherein it is assumed that the bendable segment 15 is not in contactwith the inner wall of the cavity in the respective arrangement, if notall electrodes 13, 14 arranged along the bendable segment are in contactwith the inner wall of the cavity 3. If two consecutive electrodes arein contact with the inner wall of the cavity, it is assumend that thesegment of the catheter between these two consecutive electrodes is incontact with the inner wall, i.e. that this intermediate segment forms acontact curve.

If non contact curves are used for reconstructing the cavity, theelectrical signals provided by the electrodes may be ignored. Forinstance, a bendable segment of the introduction element before thefirst proximal electrode may be used for defining non contact curves.Generally, all parts of the introduction element, which are not locatedbetween contact electrodes, can be regarded as defining non contactcurves.

The apparatus 1 is preferentially adapted to allow a user like aphysician to arrange the bendable segment at the tip 6 of the catheter 5in different arrangements within the cavity 3, wherein, after the userhas arranged the bendable segment in a desired arrangement, the curvedetermination unit 7 can determine the curve defined by the bendablesegment within the cavity 3 in this certain arrangement. In this way,different curves defined by the bendable segment within the cavity inthe different arrangements can be determined, wherein, after thesedifferent curves have been determined in the different arrangements, thecavity reconstruction unit 8 can be used to reconstruct the cavity basedon these determined curves.

The cavity 3 is influenced by cardiac motion. The apparatus thereforefurther comprises a motion signal providing unit 10 for providing amotion signal being indicative of the different cardiac phases of theheart of the person 3, wherein the cavity reconstruction unit 8 isadapted to reconstruct the cavity based on the determined curves definedby the bendable segment in the different arrangements, in particular,depending on the determined contact curves and optionally also on thedetermined non contact curves, and based on the provided motion signal.In this embodiment, the curve determination unit 7 is adapted todetermine the position of a part of the catheter 5 being in contact witha part of the person 2, which moves in accordance with the cardiaccycle, over time, thereby determining a movement of this part of thecatheter 5, wherein the motion signal providing unit 10 is adapted todetermine the motion signal depending on the determined movement. Forinstance, the curve determination unit 7 can be adapted to determine theposition of one of the contact electrodes, which can be used fordetermining whether the bendable segment is in contact with the innerwall of the cavity or not, while the contact electrode is in contactwith the inner wall of the cavity, wherein it is assumed that the innerwall of the cavity being, in this embodiment, the heart of the personmoves in accordance with the cardiac cycle. The cyclic motion of thepart of the catheter 5, which is in contact with the inner wall of thecavity 3 and which is preferentially a contact electrode, can besubdivided into several parts for defining and determining the cardiacphases of the cardiac cycle. The determined curves defined by thebendable segment in the different arrangements can be assigned to thesecardiac phases, wherein the cavity reconstruction unit 8 can be adaptedto reconstruct the cavity based on determined curves, which are assignedto a single cardiac phase only. This allows reconstructing the cavitywith reduced motion artifacts. In particular, for each cardiac phase arespective cavity can be reconstructed, wherein the differentreconstructed cavities, which correspond to different cardiac phases,can be shown temporarily consecutively on a display unit 12 forproviding a four-dimensional image of the cavity.

The curves defined by the bendable segment within the cavity 3 in thedifferent arrangements can be determined in a breathhold condition suchthat respiratory motion does not adversely affect the reconstruction ofthe cavity. However, the motion signal providing unit can also beadapted to additionally provide a further motion signal being arespiratory signal, which is indicative of different respiratory phases,wherein the cavity reconstruction unit can be adapted to reconstruct thecavity based on the first motion signal being a cardiac signal, which isindicative of the cardiac phases, and the respiratory signal. Therespiratory signal may be determined by the motion signal providing unitbased on a determined movement of a part of the catheter 5, which is incontact with an anatomical part of the person 2, which moves only inaccordance with the respiratory cycle. This movement can be determinedby the curve determination unit 7, which may determine the position ofthis part over time. The cavity reconstruction unit 8 can then beadapted to reconstruct the cavity for a certain cardiac phase and for acertain respiratory phase based on the determined curves, which areassigned to this certain cardiac phase and this certain respiratoryphase. Also in this case the cavity can be reconstructed for differentcardiac phases and for different respiratory phases, wherein theresulting reconstructed cavities can be shown temporarily consecutivelyon the display unit 12 for providing a four-dimensional reconstructedcavity.

The catheter 5 and the curve determination unit 7 are preferentiallyadapted to determine the curves defined by the bendable segment withinthe cavity 3 and also the position of further parts of the catheter 5 byoptical shape sensing.

The apparatus 1 further comprises an RF power source 11 for providingpower to the cap electrode 13 of the catheter 5, which is located at thetip 6 of the catheter 5. This allows a physician to ablate cardiactissue at a desired location within the cavity 3 depending on thereconstruction of the cavity shown on the display unit 12.

The cap electrode 13 is therefore not only used for determining whetherthe bendable segment 15 is in contact with the inner wall of the cavityor not, but also for performing an ablation procedure. In otherembodiments contact electrodes for determining, whether the bendablesegment is in contact with the inner wall of the cavity and one orseveral ablation electrodes can be different electrodes, i.e. theablation electrodes may not be used for providing the contactinformation.

In the following an embodiment of a cavity determination method fordetermining a cavity within an object will exemplarily be described withreference to a flowchart shown in FIG. 3.

In step 101 the bendable segment of the introduction element is arrangedin different arrangements within the cavity, wherein in each arrangementthe curve defined by the bendable segment is determined by a curvedetermination unit. Thus, the shape, orientation and location of thebendable segment is determined in each arrangement. Moreover,preferentially electrodes enclosing the bendable segment, in particular,being arranged along the bendable segment, are used together with acontact determination unit for determining whether the bendable segmentconforms to the inner wall of the cavity, i.e. is in contact with theinner wall of the cavity, in the respective arrangement. This allowsdetermining contact curves defined by the bendable segment inarrangements in which the bendable segment is in contact with the innerwall of the cavity, and non contact curves defined by the bendablesegment in arrangements in which the bendable segment is not in contactwith the inner wall of the cavity.

In step 102 the cavity is reconstructed from the determined curves by acavity reconstruction unit. In particular, an adaptable model may beadapted to the contact curves or the contact curves may be interpolated,in order to reconstruct the cavity.

The apparatus is preferentially adapted to perform a minimally invasive,transcatheter procedure. During those procedures the physician, forinstance, a surgeon or a cardiologist, cannot observe tools and anatomywith the naked eye. Real-time imaging modalities such as x-raymodalities or ultrasound modalities provide partial solutions to thisproblem, but they have their own limitations. In some interventionalprocedures like atrial fibrillation ablation such imaging modalities maybe skipped in the prior art, wherein instead a positioning device like amagnetic-based positioning device attached to an ablation catheter maybe used to reconstruct the cavity of, for instance, the left atrium.However, using such a positioning device has at least two majorproblems. The use of a single position or of even few positions forreconstructing the cavity yields scarce data, the acquisition times arerather long and the modeling quality it relatively low.

The apparatus described above with reference to FIGS. 1 and 2 istherefore preferentially adapted such that the positioning device can bereplaced by a shape sensing device, which enables the reconstruction tobe based on curves, rather than points, in a much faster fashion. Inparticular, shape sensing technology is preferentially used, in order torecover very quickly the shape of the cavity. Preferentially, the shapeof the device, i.e. the shape of the bendable segment, is collected,while the device is moved inside the target cavity. As the device liesinside the cavity, the cavity surface can be recovered as the “outersurface” of the collected shapes. In particular, a catheter may be movedrapidly and in a more or less random fashion to quickly get the bulk ofthe cavity, for instance, of the left atrium of a heart of a person. Theoutcome of the corresponding algorithm can then be used as a rough mapto guide the catheter into areas where the acquisition should berefined, for instance, because of a particularly high interest in thisarea and/or because the area is more difficult to access due to largercurvatures which could have hampered a correct acquisition during theinitial sweep. Higher curvatures may be present, for instance, inpulmonary veins.

For determining whether a point lying outside the acquired shapes, i.e.outside the set of determined curves defined by the bendable segment inthe different arrangements within the cavity, belongs to the cavity ornot, the apparatus can be adapted to use a regularity assumption. Thisregularity assumption can be expressed, for example, as a singlemathematical opening or closure operation, or the regularity assumptioncould be a more complex and knowledge-based one based, for example, on amesh template of the targeted cavity.

The apparatus is preferentially adapted to produce a consistent output,even if the cavity moves and/or deforms. Especially if the apparatus isused in cardiac applications, the apparatus can be adapted to handlewith the deformations during the cardiac cycle and to considerrespiratory motion as well. As the shape of the heart chambers deformsduring the cardiac cycle, determined curves, which correspond todifferent cardiac phases, are preferentially not mixed. The apparatuscan be adapted to reconstruct a three-dimensional model at a specificcardiac phase or at an indefinite cardiac phase, if the model is basedon temporal averaging. The apparatus can also be adapted to reconstructa four-dimensional model, i.e. a temporarily dependent spatiallythree-dimensional model of the cavity.

For identifying the cardiac phase and for assigning the identifiedcardiac phase to the respective determined curves the above describedmethod can be used, which is based on the determination of the movementof a part of the introduction element, which moves in accordance withthe cardiac cycle, because it is in contact with, for instance, an innerwall of a heart chamber. However, a cardiac signal can also be providedby other means. For example, a known electrocardiograph can be used forproviding a cardiac signal. Moreover, it is also possible to determinethe cardiac phase from the electrocardiography signal and from thedetermined motion of the part of the introduction element, which is incontact with, for instance, an inner wall of the heart chamber.

In order to mitigate a possible effect of respiratory motion on thequality of reconstructing the cavity, the acquisition, i.e. thedetermination of the curves defined by the bendable segment in thedifferent orientations, can be performed at a given breathhold.

Alternatively, the respiratory motion can be estimated using the shapeof the introduction element, in particular, of the catheter, while apart of the introduction element lies against a part of the anatomy ofthe living being, from which respiratory motion can be estimated, inparticular, which experiences pure respiratory motion.

Also a second shape sensing introduction element, in particular, asecond shape sensing catheter, can be used in a similar fashion fordetermining respiratory motion. In this case, the first introductionelement does not need to be guided through an area experiencing, forinstance, pure respiratory motion, because the second shape sensingintroduction element already provides the respiratory motion, which canbe used for generating a respiratory signal. For example, in atrialfibrillation ablation procedures the coronary sinus catheter can be usedas the second shape sensing introduction element in combination withheart motion cancellation techniques.

The respiratory motion can also be determined using other techniqueslike a respiratory belt, analyzing a video showing a part of the person,for instance, the thorax performing respiratory motion, et cetera.

Although in embodiments described above a possibly adverse effect on thereconstruction of the cavity due to respiratory motion is reduced bydetermining the curves defined by the bendable segment in the differentarrangements in a breathhold condition or by reconstructing the cavityfor a certain respiratory phase based on curves defined by the bendablesegment in the different arrangements, which correspond to this certainrespiratory phase, the adverse influence of the respiratory motion canalso be reduced in another way. For instance, the determined curvesdefined by the bendable segment in the different arrangements can becorrected by a translational operation in accordance with the determinedrespiratory motion, wherein the cavity can be reconstructed based on thecorrected curves.

The apparatus is preferentially adapted to model or fit an anatomicalpart, i.e. an anatomical cavity within a living being, based on ashape-sensing enabled catheter, preferentially without furtherrequirements. It is further preferred that the apparatus uses largesegments of the catheter for the determination of the cavity within theliving being, i.e. the apparatus does preferentially not only use pointpositions as in the case of known electromagnetic tracking techniques,but the apparatus uses larger segments, which are larger than points on,for instance, a catheter.

The apparatus is preferentially adapted to use simultaneously shapesensing technology and multiple contact electrodes, wherein the contactof an electrode of the introduction element with the cavity is inferredbased on the electrical signal measured by the respective electrode.

In an embodiment it is assumed that, when two electrodes are in contact,a part of the introduction element, i.e. the bendable segment, lyingbetween them is also in contact with the cavity such that the shape ofthe introduction element between the two electrodes provided by shapesensing, which may define a respective contact curve, can be used forreconstructing the cavity. If the cavity curvature is very high in someareas, this assumption may be violated, thereby producing an undersegmentation of the cavity. This under segmentation of the cavity can becorrected by inserting the introduction element inside the cavity. Forinstance, a catheter tip can be navigated to these areas and theposition of the catheter tip can be determined, while the catheter tipis in these areas. These positions can be used together with thedetermined curves defined by the bendable segment in the differentarrangements for reconstructing the cavity, wherein the cavity can bereconstructed such that the determined curves defined by the bendablesegment in the different arrangements and also the determined positionsof the catheter tip in the areas with the relatively high curvature arewithin the cavity. For instance, a cavity model can be adapted to thesepositions such that the cavity model encloses the different curvesdefined by the bendable segment and the positions of the catheter tipand such that the adapted cavity model conforms to these positions asgood as possible.

Although in above described embodiments the introduction elementcomprises electrodes for determining whether the bendable segment is incontact with the inner wall of the cavity, in other embodiments theintroduction element may not comprise electrodes for determining thiscontact information, in particular, the introduction element may notcomprise any electrode or only electrodes for other purposes. In thiscase it is generally not known whether determined curves defined by thebendable segment are contact curves or non contact curves. However, alsowithout this contact information the cavity reconstruction unit canreconstruct the cavity, for instance, by adaptating a cavity model, inparticular, an anatomical cavity model, to the set of determined curvessuch that the determined curves are within the adapted cavity model andsuch that the adapted cavity model conforms as good as possible to theouter curves of the determined curves, or by performing, for instance, amorphological opening or closing of the set of curves.

The apparatus can also be adapted to record coordinates of curves thatare not in contact with the cavity, i.e. to record non contact curves,in order to provide an indication of what constitutes the inside of thecavity. This could also be used at a final step to close holes in thereconstructed cavity due to non responsive tissues like scars or ablatedareas.

The apparatus can be adapted to model or fit an anatomical part based onan introduction element with both shape sensing fibers and multipleelectrodes, wherein shapes of a cavity can be reconstructed based onentire curves of the introduction element. The apparatus ispreferentially adapted to be used in atrial fibrillation ablationprocedures, in order to reduce the patient exposure to radiation, bothbefore the operation and also after the operation.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality.

A single unit or device may fulfill the functions of several itemsrecited in the claims. The mere fact that certain measures are recitedin mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

Determinations like the determination of the cavity, i.e. thereconstruction of the cavity, the determination of the different curvesdefined by the bendable segment within the cavity in the differentarrangements, the determination of the motion signal, et ceteraperformed by one or several units or devices can be performed by anyother number of units or devices. The determinations and/or the controlof the cavity determination apparatus in accordance with the cavitydetermination method can be implemented as program code means of acomputer program and/or as dedicated hardware.

A computer program may be stored/distributed on a suitable medium, suchas an optical storage medium or a solid-state medium, supplied togetherwith or as part of other hardware, but may also be distributed in otherforms, such as via the Internet or other wired or wirelesstelecommunication systems.

Any reference signs in the claims should not be construed as limitingthe scope.

The invention relates to a cavity determination apparatus fordetermining a cavity within an object, in particular, for determiningthe location and dimensions of a heart chamber within a person. Abendable segment of an introduction element is arranged within thecavity in different arrangements, wherein curves defined by the bendablesegment in the different arrangements are determined by a curvedetermination unit. A cavity reconstruction unit reconstructs the cavitybased on the determined curves. Thus, not only single small locationswithin the cavity are acquired and used for reconstructing the cavity,but larger curves. A lot of spatial information can therefore beacquired and used very fast. This allows reconstructing the cavity withimproved quality in a relatively short time.

The invention claimed is:
 1. A cavity determination apparatus fordetermining a cavity within an object, the apparatus comprising: anintroduction element for being introduced into the cavity, wherein theintroduction element comprises (a)(i) an optical shape sensing catheterwith a bendable segment for being arranged within the cavity indifferent arrangements and (a)(ii) at least two electrodes between whichthe bendable segment is located, wherein the at least two electrodescomprise a tip electrode located at a tip of the optical shape sensingcatheter, and one or more ring electrodes spaced from the tip electrodealong the bendable segment of the optical shape sensing catheter; acurve determination processor configured to determine a set of curvesvia optical shape sensing of the bendable segment of the optical shapesensing catheter, wherein each curve is defined by an introduction ofthe bendable segment within the cavity in a respective arrangement ofthe different arrangements; a contact determination processor,electrically coupled to the at least two electrodes, configured todetermine contact information indicating whether the bendable segment isin contact with an inner wall of the cavity in response to electricalsignals received from the at least two electrodes; a cavityreconstruction processor configured to reconstruct the cavity inresponse to the determined set of curves, wherein the cavityreconstruction processor reconstructs the cavity, via (b)(i) aregularization in response to the set of the determined curves and(b)(ii) a morphological opening or closing of the set of the determinedcurves to estimate which points of the set of the determined curves lienecessarily within the cavity, wherein the cavity reconstructionprocessor is further configured to (c)(i) determine whether a determinedcurve is a contact curve in response to the contact information and(c)(ii) reconstruct the cavity in response to determined contact curvesand respective positions of the tip electrode: and a display device,operatively coupled to the cavity reconstruction processor, configuredto display a representation of the reconstructed cavity.
 2. Theapparatus as defined in claim 1, wherein the cavity reconstructionprocessor is further configured to reconstruct the cavity in response tothe determined curves defined by the bendable segment in the differentarrangements being determined within the reconstructed cavity.
 3. Theapparatus as defined in claim 2, wherein at least in some of thedifferent arrangements the bendable segment is in contact with the innerwall of the cavity, wherein corresponding curves comprise contactcurves.
 4. The apparatus as defined in claim 3, wherein the cavityreconstruction processor is further configured to reconstruct the cavityin response to walls of the reconstructed cavity corresponding to thecontact curves.
 5. The apparatus as defined in claim 3, wherein, atleast in some of the different arrangements, the bendable segment is notin contact with the inner wall of the cavity, wherein correspondingcurves defined by the bendable segment comprise non contact curves, andfurther wherein the cavity reconstruction processor is furtherconfigured to reconstruct the cavity in response to both the contactcurves and the non contact curves.
 6. The apparatus as defined in claim5, wherein the cavity reconstruction processor is further configured toreconstruct the cavity with the non contact curves being determinedwithin the reconstructed cavity.
 7. The apparatus as defined in claim 5,wherein the cavity reconstruction processor is further configured todetermine whether a determined curve comprises a non contact curve inresponse to the contact information.
 8. The apparatus as defined inclaim 1, wherein the cavity reconstruction processor is furtherconfigured to adapt a cavity model for reconstructing the cavity inresponse to the determined curves defined by the bendable segment in thedifferent arrangements.
 9. The apparatus as defined in claim 1, whereinthe cavity reconstruction processor is further configured to interpolatethe determined curves defined by the bendable segment in the differentarrangements for reconstructing the cavity.
 10. The apparatus as definedin claim 1, wherein the object is a living being, wherein the cavity isinfluenced by at least one of cardiac motion and respiratory motion, theapparatus further comprising: a motion signal processor, operativelycoupled to the cavity reconstruction processor, configured to determinea motion signal, indicative of at least one of a) different cardiacphases and b) different respiratory phases of the living being, based ona determined movement in position of a part of the optical shape sensingcatheter being in contact with a part of the living being which moves inaccordance with at least one of a cardiac cycle and a respiratory cycle,over time, and wherein the cavity reconstruction processor is furtherconfigured to reconstruct the cavity in response to both the determinedcurves defined by the bendable segment and the motion signal.
 11. Acavity determination computer program for determining a cavity within anobject, wherein the computer program is characterized by program codemeans for causing a cavity determination apparatus as defined in claim 1to carry out following steps, when the computer program is run on acomputer provided with one or more processors for controlling the cavitydetermination apparatus: determining, via a curve determinationprocessor, a set of curves, each curve being defined by a bendablesegment of an optical shape sensing catheter of an introduction elementintroduced into the cavity in a respective arrangement of differentarrangements within the cavity, wherein the optical shape sensingcatheter includes at least two electrodes between which the bendablesegment is located, wherein the at least two electrodes comprise a tipelectrode located at a tip of the optical shape sensing catheter, andone or more ring electrodes spaced from the tip electrode along thebendable segment of the optical shape sensing catheter; determining, viaa contact determination processor, contact information indicatingwhether the bendable segment is in contact with an inner wall of thecavity in response to electrical signals received from the at least twoelectrodes; reconstructing, via a cavity reconstruction processor, thecavity from the determined curves, wherein the cavity reconstructionprocessor reconstructs the cavity, via (a)(i) a regularization inresponse to the set of the determined curves and (a)(ii) a morphologicalopening or closing of the set of the determined curves to estimate whichpoints of the set of the determined curves lie necessarily within thecavity, wherein reconstructing the cavity further includes (b)(i)determining whether a determined curve is a contact curve in response tothe contact information and (b)(ii) reconstructing the cavity inresponse to determined contact curves and respective positions of thetip electrode; and displaying, via a display device operatively coupledto the cavity construction processor, a representation of thereconstructed cavity.